Apparatus for controlling the load on an x-ray tube



Dec. 19, 1944. A. F. JEANS A 2,355,554

APPARATUS FOR CONTROLLING THE LOAD ON AN X-RAY TUBE Filed Sept. 29, 1943 2 Sheets-Sheet l jfzg. 1..

5O 62.565 '80 9O KV ARTHUR H JEANS INVENTOR.

A T TORNEY Dec. 19, 1944. A. F. JEANS 2,365,554

APPARATUS FOR CONTROLLING THE LOAD ON AN X-RAY TUBE Filed Sept. 29, 1943 2 Sheets-Sheet 2 SEC 5 ARTHURIZ JEANS INVENTOR.

A'IIURNEY The contacts and. switch Patented Dec. 19, 1944 APPARATUS FOR! CONTROLLING N X-RAY TUBE.

Arthur Frederick Jeans, London,

THE I-ZOAD England, as.-

slgnor to The Hartford National Bank. and

Trust Company. Hartford; Conn., as trustee Application September: 29, In Great; Britain 4 Claims.

The: load on. an X-ray tube isz determinedz by three variables", viz: IcV, mA, and. time, and. in

general diagnostic X-ray apparatus is provided" I with separate means for controlling the values:

of each. In order: to: obtain, best radiographic. results. with a given. X-ray: tube; it. is necessary in many cases to operate the: tube at maximum permissible load. If an X-ray' tube is to operate at maximum permissible load there; must be a. definite relationship between the three variables. This relationship can conveniently'be represented graphically by a series of characteristic curves plotted with one ofthe variables asordinates and another of the'variables asabscissae, each curve being for a. different valueof thethird': variable. The object of the present invention is to provide forthe automatic correlating of the three variables in such a manner as to ensure thatovereloading can never occur whileat the same time enabling close approximation to maximum tolerable load to be achieved. With this object in view, the present invention provides an arrange ment for controlling the load on an X-ray tube in which the means for controlling the three variables are separately adjustablebutare interlocked insuchv manner that the tube'cannot beoperated: at settings which would" bring about overloading ofv the tube. all permissible combinations of the three vari ables, viz: kV, mA and time, are possible, or it maybe such that after free selection of two: variables (e. g. krV and. time) the third variable (mA) is automatically selected. In; thelatter case the load approaches the full. permissible load for all combinations of the freely selected variables;- According to the present invention, the controls for the three variables are; each associated: with a device which assumes a; position corresponding. to the setting of the associated. control. Con

tacts selected by the device associated with one of the controls are connected with contactsselected by the device associated with another of the controls by means of a. multi-way connector switch associated with the third. control device.

tube characteristic as t provide a through connection only when the setting of..the three con, trols is such as .to fall within the permissible load. The through connection so provided forms part of a circuit comprising a safety relay controlling the working circuit of the X-ray tube.

In order that the invention may be morereadily understood, reference. will now be made to. the accompanying drawings in which:

Fig. 1 is a graphical representation. of typical relationships between the three variables, viz: mA,.kV and time.

The arrangement may be such that are. so: related to the 1943', Serial No..5lJ.4,320 June 13; 1942' The switch positions.- are marked in the draw-- Fig; 2 is a diagrammatic representation of a 7 preferred construction for carrying out the present invention.

In- Fig. 1, themA val'uesare plotted asordinates and" the MT values. as abscissae, and separate: curves are drawn for a seriesofdifierent. values.- of the exposure time in seconds;v From these. curves; it is readily possible to determine the maximum permissible value of any. one variable.- for predetermined values of the other: two variables. Thus, for example, the ordinates a; 11,, 0;

etc. represent the maximum permissible mA- values for a lcV of 62.5 and an exposuretime. of

0125, 0.3, 0.4, etc. second respectively- In practice, the nearest lower available mA value to; the permissible valuehasto be chosen.

In the diagrammatic 2;. the: switch. ST'is a.

. multiple-contact switch mechanically coupled to the time switch control in; the X-ray'apparatus;

ings with numbers representing the exposure, time in seconds-as set by the time. switch. The central part of Fig. 2; marked IcV,.represents a rotary drum coupled with the. 10V selector switch- The drum: itself is. indicated in Fig. 2 and is shown? fragmentaril'y in theupper portion of the figure, whereas the central portion is a developed view. 0n the drum, contact studs. are provided. which; are arranged in rows: extending round the. periphery of the drum and in rows extending lengthwise of the drum. In the developed view, these contact studs are represented by dots. Each vertical row of dots representsa given kV adjust ment. On the left hand side of. Fig.2 are shown brushesidentified as. mA 500,400, 300, etc.: these brushes; which are connected each. to one con.- tact of a switch SmA, are adapted to cooperate each with. one of the horizontalrows-of dots (i. e.

one of theperipheral rows of contact studs): and

tomake' connection with one. contact only in the; row in anygiven setting of the drum. The switch SmzA is a multiple-contact switch coupled with the mA selection switchin the same way as the switch ST'is coupled with the time switch. Consequently each horizontal row of dots represents a given mAv adjustment. Thus: the co-ordinates of. each dot define given mA. and V adjustments. The maximum. time setting. permissible is. de termined from the characteristic, curves of. Fig. 1. All the contact studs requiring the same time setting are connectedtogether on the drum, as indicated by the lines which for the. greater part extend obliquely upwardly from right to left. in Fig. 2. These connecting leads are. each connected to a slip ring and the slip. rings serveto give a. permanent connection between each connecting lead and the corresponding. contact on the. switch. ST.

The switch ST, the drum kV, the switch. SmA and: a relay R. arev connected in series with. a sourceof' current. The; relay R serves. to control the main circuit of the X-ray tube, so that the main circuit is broken if the relay R is not enermum loading. Equally rangement as described To enable the operation of the arrangement ad- 3 cording to Fig. 2 to be more readily understood certain specific examples will be discussed. Assuming that, as shown, that the mA brushes make contact with the ver tical row of contact studs (corresponding to 45 V. If then the time control is set for 1.5 seconds, the switch ST takes up the full-line position and the connection through the drum follows the lead shown by a heavy line. This lead extends to the 250 mA brush. If, therefore, the switch SmA is so set as to be connected with this brush, the circuit of relay Ris completed, R is energized and the main circuit is not disabled. Consequently with this admissible setting of the three controls for time, kV and mA the X-ray tube can be operated. If, however, the mA select-or were set to a higher value without alteration in the kV e. -g., the mA selector is set to 500 mA, then as shown by thebroken-line lead through the RV drum, the appropriate setting of the time switch (assuming IN to remain at 45) is 0.5 see.

In addition to the selecting arm, the switch ST preferably carries a wiper arm which moves with the selecting arm and connects in the circuit of the relay R all the timer leads corresponding to time adjustments greater than the selected time. 'In Fig. 2, this wiper arm i indicated by the arcuate member STW. Owin to the action of the wiper arm the circuit of the relay R is completed at any setting of the mA selector not exceeding the permissible maximum current corresponding to the IN and time settings. It will be appreciated that the leads through the drum as shown in Fig. 2 are for the case in which the switch ST is equipped with the wiper STW. In the absence of the wiper STW each lead would have to extend round the full working periphery of the drum (as in the case of the 0.8 sec. .lead) and not only part of. the way (as in the case of the 1.0 sec. lead).

It will be apparent that instead of selecting the mA setting by the conventional hand control, the completion of the circuit through the switch ST and one of the leads extending through the drum to one of the brushes mA 500 etc., may be made to operate a relay ,which automatically sets the mA selector to the permissible maximum. Alternatively the relay could introduce a mechanical stop into the path of a man-- ually movable mA selector handle to prevent movement of the handle into a position beyond the setting corresponding ,to the permissible maxithe circuit may be used to actuate a visual indicator showing the permissible maximum mA value for the previously selected values of IN and time.

It will be appreciated that although reference has been made to kV control, mA control and time control respectively in relation to specific components of the interlocking control arabove with reference to Fig. 2, any one component could be associated with any desired factor, but the described association is believed to be the most advantageous.

I claim:

1. Apparatus for controlling the main circuit loading potential-, currentand time variables the 70V drum is so set and time adjustments, 7

applied to an X-ray tube, comprising means for selecting one of a plurality of predetermined values of one of said variables and comprising a switching member having a plurality of contacts, each contact corresponding to one of said values of said one of said variables, means for selecting one of a pluralits of predetermined values of another of said variables and comprising a switching to one of said v ing member having a plurality of contacts arranged in a plurality of sets with the corresponding contacts of each set being connected together, the contacts of each set each correspondalues of the second of said variables and the number of sets of contacts corresponding to the number of values of the first of said variables, means for selecting one of a plurality of predetermined values of the third of said variables and comprising a switching member having a plurality of contacts each corresponding to one of a plurality of values of said third variable and each being connected to a contact of said second switching member at a point at which the product of the three variables represented by the contact of said second switching member is within the maximum permissible loading of the X-ray tube, the three said switching members being connected in series, and means energized through said switches to control the on and off operation of the main circuit of the X-ray tube.

2. Apparatus as claimed inclaim 1 in which the contacts of said third switching member are each connected to a contact of said second switching member at a point at which the product of the three variables represented by the contact of said second switching member is substantially equal to maximum permissible loading of the X-ray tube.

3. Apparatus as claimed in claim 1 in which said second switching vmember is constituted by a rotatable drum and the contacts of the switching member are arranged in rows extending peripherally and longitudinally on the surface of the drum; the number of peripheral rows corresponding to the number of contacts of the first switching member and the number of longitudinal rows corresponding to the number of selectable values of said second variable.

4. Apparatus as claimed in claim 1 in which said second switching member is constituted by a rotatable drumand th contacts of the switching member. are arranged in rows extending peripherally and longitudinally on the surface of the drum, the number of peripheral rows corresponding to the number of contacts of the first switching member and the number of longitudinal rows. corresponding to the number of selectable values of said second variable, in which a plurality of brush members are individually connected to the contacts of said first, switching 

